A product marketed with an interdigitated base and top member held together by a retaining ring is marketed by Raychem Corporation under the name FOSC.RTM.(B) Closure. This closure is, at least in part, described in PCT International Publication No. W090/08336 and Great Britain priority application No. 800932.8 the former of which was filed Jan. 17, 1990, and the later of which was filed Jan. 17, 1989. Both these applications are incorporated herein by reference for all purposes. Although this product functions extremely well, the castellated flanges, i.e., interdigitated base and top members, which are locked together by a circular, round in cross-section retaining ring contained within a groove extending through the flanges, exhibit certain tendencies to pull apart through the deflection of certain of the flanges and the ring popping out of the groove at temperatures of about 70.degree. C. The retaining ring exerts a force on the castellated flange off center from the neutral axis, i.e., the axis running through the base of the groove. This produces a bending moment in the flange which causes flange deflection. The deflection may be great enough such that the ring pops out of the groove allowing the base to separate from the domed top member. Thus, it would be highly desirable to have a retaining ring and structure which avoids this problem for high temperature applications, i.e., about 70.degree. C., to extend the useful temperature range of the product.